US Xperia support both T-Mobile and AT&T?

When the Sony Ericsson Xperia was announced, the specs originally mentioned rather unusual frequency coverage, for both the more common AT&T and the muchÂ less frequently used T-Mobile 3G. These specs disappeared the the Xperia website for a while, but now appears to have returned with a vengeance.

In the published specs for the US version the specifications now list:

UMTS tri-band UMTS 850 UMTS 900 UMTS 1700 UMTS 1900 UMTS 2100

This has led to rife speculation in the usual forums that the Xperia will also launch on the T-Mobile network. While we have no confirmation on this, if the above is true and not an error by SE, it would at the very least mean US users have a real choice as to which GSM network to use, vs being always tied to AT&T.